Liquid crystal compositions

ABSTRACT

A NEMATIC LIQUID CRYSTAL COMPOSITION HAVING A VERY BROAD MESOPHASE COMPRISING A MIXTURE OF AT LEAST ONE COMPOUND OF THE FORMULA:   (4-R-PHENYL)-CH=N-(1,4-PHENYLENE)-R1   WHEREIN R AND R1 ARE RADICALS SELECTED FROM THE GROUP CONSISTING OF A SATURATED ALKOXY RADICAL AND AN ALKYL RADICAL, EACH HAVING FROM 1 TO 9 CARBON ATOMS AND ONLY ONE OF R AND R1 IS ALKYL; AT LEAST ONE COMPOUND OF THE FORMULA:   (4-R2-PHENYL)-CH=N-(1,4-PHENYLENE)-R3   WHEREIN R2 AND R3 ARE RADICALS SELECTED FROM GROUP CONSISTING OF A SATURATED ALKOXY RADICAL HAVING FROM 1 TO 9 CARBON ATOMS AND A SATURATED ACYLOXY RADICAL HAVING FROM 2 TO 5 CARBON ATOMS, AND ONLY ONE OF R2 AND R3 IS AN ALKOXY RADICAL; AND AT LEAST ONE COMPOUND OF THE FORMULA:   (4-(R4-(COO)X-)PHENYL)-OOC-(1,4-PHENYLENE)-(OOC)Y-R5   WHEREIN R4 AND R5 ARE SATURATED ALKOXY RADICALS OF FROM 1 TO 9 CARBON ATOMS, ONE OF X AND Y IS 0 AND THE OTHER IS 1.

United States Patent 3,772,210 LIQUID CRYSTAL COMPOSITIONS Marcello Lodolini, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y.

No Drawing. Continuation-impart of abandoned application Ser. No. 215,090, Jan. 3, 1972. This application Feb. 14, 1972, Ser. No. 226,312

Int. Cl. G01n 31/00 U.S. Cl. 252-408 11 Claims ABSTRACT OF THE DISCLOSURE A nematic liquid crystal composition having a very broad mesophase comprising a mixture of at least one compound of the formula:

wherein R and R are radicals selected from the group consisting of a saturated alkoxy radical and an alkyl radical, each having from 1 to 9 carbon atoms and only one of R and R is alkyl; at least one compound of the formula:

wherein R and R are radicals selected from the group consisting of a saturated alkoxy radical having from 1 to 9 carbon atoms and a saturated acyloxy radical having from 2 to carbon atoms, and only one of R and R is an alkoxy radical; and at least one compound of the formula:

wherein R and R are saturated alkoxy radicals of from 1 to 9 carbon atoms, one of x and y is 0 and the other is 1.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 215,090, filed Jan. 3, 1972, now abandoned.

FIELD OF THE INVENTION This application relates generally to liquid crystal compositions and more particularly to nematic liquid crystal compositions having a broad mesophase.

BACKGROUND OF THE INVENTION Nematic liquid crystal compositions are used in various electro-optical devices which involve the modulation of light, such as light valves and optical display devices. Such light valves are controlled by an electric field and operate when the liquid crystal material is in its mesomorphic state. Generally, when no electric field is applied to the nematic liquid crystal material, the device containing a thin layer of this material is relatively transparent to light. When an electric field is applied to the liquid crystal material above a threshold value, which value depends upon the particular liquid crystal composition, the device appears to become opaque in the region of the field. This opacity is due to the scattering of light by domains of the liquid crystal molecules which align themselves in the field.

The electro-optical effect due to alignment of domains of the nematic liquid crystal molecules in an electric field may be employed in transmissive, reflective, or absorptive-type fiat-panel displays, in light shutters, and in other applications.

Compositions having a mesomorphic state or mesophase have wide melting or transition points. The first transition point is at the transition from the crystalline solid state to the mesomorphic state. The second transition point is at the transition from the mesomorphic state to the isotropic liquid. Between these temperatures the compound exists in the mesomorphic or liquid crystalline state in which it behaves both as a liquid in that it flows and exists in drops that coalesce, and as a solid in that it is optically or electrically anisotropic and has a structural order in one or two dimensions.

Nematic liquid crystals are electrically and magnetically anisotropic. On surfaces such as glass, the nematic phase generally adopts a characteristic threaded texture visible between crossed polaroids. This texture is thought to consist of many domains or clusters in which the liquid crystal molecules have a fixed orientation. According to the cluster theory of nematic liquid crystals, the clusters are normally randomly oriented, accounting for the light scattering properties and for the turbid appearance of a fairly large volume. Each cluster is birefringent and is about 10" cm. in size. Upon applying an electric or magnetic field to a layer of mesomorphic crystals, the clusters tend to become oriented in a particular direction, thereby changing the light-scattering and birefringent properties of the layer. The degree of orientation is dependent upon the magnitude of the applied field. Hence, the light-scattering properties and birefringent properties of a volume of nematic liquid crystalline material can be modulated with an electric or magnetic field.

Where the use of a liquid crystal composition is dependent on changes in orientation of the composition while in the mesomorphic state, the composition must be above the crystal-mesomorphic transition temperature. Prior art liquid crystal compositions have relatively high crystal-mesomorphic transition temperatures. Therefore, heat must be provided to keep the composition in the mesomorphic state. The higher this transition temperature, the greater the cost of heating. Another disadvantage of the prior-art compositions is that the temperature range in which the composition remains in the liquid crystalline state is relatively small. This may require means to control the heating.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved crystal mixture. A further object of this invention is to provide a nematic liquid crystal mixture having a wide mesophase. Another object of this invention is to provide a liquid crystal composition having a mesomorphic state at room temperature. A further object of this invention is to provide a nematic liquid crystal com position having a crystal-mesomorphic transition temperature below room temperature. Another object of this invention is to provide a liquid crystal composition that does not require careful temperature control.

These and other objects and advantages are accomplished by a mixture of at least one compound of the Forwith at least one compound of the Formula II:

and of at least one compound of the Formula III:

wherein R, R R R R and R and x and y are as hereinafter defined.

3 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The family of nematic liquid crystal compositions provided by this invention include at least one and preferably two compounds of the following Formula I:

TABLE I Compound:

1 C2H50 (CH2)3CH3 2 CH3(CH2)30 CH2)3CH:

CHa(CHz)3O C 115 CH (CH2)4O OzHs H O CaHfl CzHs OCH: O(CHz)aCHs O(CH2)3CH 002135 0081111 The foregoing compounds are only exemplary of the compounds which may be incorporated into the nematic liquid crystal composition of this invention. Compounds of this type are disclosed in and prepared by the methods disclosed in German patent application No. 2,017,727 published Oct. 29, 1970, incorporated herein by reference. Compounds having the structure of Formula I are preferably present in amounts of about 10 to about 20 weight percent of the total mixture. In a still further preferred embodiment, two compounds of this structure are present in about equal amounts of, for example, about 7.5 weight percent each.

The nematic liquid crystal compositions provided by this invention include at least one and preferably two compounds of the following Formula II:

wherein R and R are radicals selected from the group consisting of a saturated alkoxy radical having from 1 to 9 carbon atoms and a saturated acyloxy radical having from 2 to carbon atoms. When R is a saturated alkoxy radical, R is a saturated acyloxy radical and vice versa.

Exemplary of compounds of Formula II are p-methoxybenzylidene p aminophenyl butyrate; p-butoxybenzylidene-p-aminophenyl propionate; and p-methoxybenzylidene-paminophenylvalerate. Other examples of compounds of Formula II which may be used in this nematic 4 Compounds of this type are disclosed in and prepared by the methods disclosed in US. Pat. No. 3,540,796, incorporated herein by reference.

Compounds having the structure of Formula II are preferably present in the nematic liquid composition in amounts of about 60 to about weight percent of the total mixture. In a still further preferred embodiment, two compounds of this structure are present in the compositions of this invention; the total combined weights of these two compounds representing about 75 percent of the total weight of said compositions at about a 3:2 mole ratio of either compound to the other.

The liquid crystal compositions of this invention include at least one'and preferably only' one compound of the following Formula III:

wherein R and R are saturated alkoxy radicals having from 1 to 9 carbon atoms. x and y differ and are selected from the group consisting of 0 and 1. Typical examples of useful alkoxy radicals are set out above (in the description of substituents in Formula I), and preferably having 1 to 5 carbon atoms.

Exemplary of compounds of Formula III is butyl-p- (p-ethoxyphenoxycarbonyl)phenyl carbonate. In a particularly preferred embodiment of this invention, a compound of this structure is present in an amount of about 5 to about 20 weight percent of the total mixture, and desirably about equal to one of the compounds of Formula I.

In order for the nematic liquid crystal compositions of this invention to produce best results, the compounds forming the composition are preferably first purified so as to remove particulate impurities, as well as impurities within the crystalline phase. One measure of purity is the resistivity of the compounds. The pure compounds disclosed herein generally have resistivities in the range of 10 -10 ohm-centimeters.

The mixtures are prepared by careful recrystallizations of each compound until a constant and reversible mesomorphic range is attained. The color of each compound is reduced to a minimum to achieve a mixture with minimum color. The compounds are then weighed, mixed, and melted together and stirred to obtain a homogeneous nematic melt. The resulting mixture is filtered to remove trace insoluble material, then stirred over a molecular sieve to remove traces of moisture. Desirably the compounds are mixed so that portions denominated a, b and c (corresponding to Formulas I, II and IH, respectively) are present in a Weight ratio of 6: 16:3, respectively.

The first five of the following examples will illustrate the preparation of the compounds comprising a preferred nematic liquid crystal mixture.

EXAMPLE 1 p-Methoxybenzylidene-p-aminophenyl butyrate is prepared by the esterification of p-methoxybenzylidene amino phenol with butyric anhydride. The reaction is carried out in a refluxing benzene solution in the presence of pyridine. The resulting compound is recrystallized from an isopropyl alcohol solution.

EXAMPLE 2 p-Butoxybenzylidene-p-aminophenylpropionate is prepared by refluxing a solution of p-butoxylbenzylidene amino phenol with propionic anhydride in the presence of pyridine. The resulting ester is purified by recrystallizing from hot isopropanol.

EXAMPLE 3 Butyl p-(p-ethoxyphenoxycarbonyl)phenyl carbonate is prepared by the esterification of p-hydroxybenzoic acid with p-ethoxyphenol to form p-ethoxyphenyl p-hydroxybenzoate. This intermediate is treated with butyl chloroformate in the presence of pyridine or triethylamine to yield the desired product.

EXAMPLE 4 N(p-butoxybenzylidene)ppropylaniline is prepared by treating p-propylaniline with p-butoxybenzaldehyde in alcohol. The product is recrystallized from alcohol.

EXAMPLE 5 A nematic liquid crystal composition is prepared by mixing 488 parts of the product of Example 1, 319 parts of the product of Example 2, 75 parts of the product of Example 3, 75 parts of the product of Example 4 and 75 parts of the product of Example 5. The mixture was melted and stirred to obtain a homogeneous nematic melt. The resulting melt was filtered through a Super-Cel mat to remove trace insoluble materials and then stirred over a Linde 4A molecular sieve to remove traces of moisture. The resulting composition had the following physical and electro-optical properties. All measurements were made in a .5 x .5 cm. cell of NESA coated glass with a .5 mil Teflon spacer.

Mesomorphic range (by differential scanning calorimetry) 1597 C.

Transmittance in the saturated state Optimum voltage 0.19 in 8 milliseconds. 40 volts DC; 50-60 volts AC. Threshold voltage 4 volts. Contrast ratio at 38 volts DC 39:1. Contrast ratio at 24 volts DC 26:1.

Readily supercools below C.

By rise time, it is meant the time necessary to align the domains. By decay time, it is meant the time it takes after removal of the applied field for the liquid crystals to return to its random state.

It can be seen from the foregoing that liquid crystal compositions of extremely wide mesomorphic range can be obtained by mixtures of the various compounds set forth above.

The invention has been described in detail with particu lar reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

What is claimed is:

1. A nematic liquid crystal composition comprising a mixture of at least one compound of the formula:

wherein R and R are radicals selected from the group consisting of a saturated alkoxy radical and an alkyl radical, each radical having from 1 to 9 carbon atoms, when R is an alkoxy radical, R is an alkyl radical, and vice versa, with at least one compound of the formula:

wherein R and R are radicals selected from the group consisting of a saturated alkoxy radical having from 1 to 9 carbon atoms and a saturated acyloxy radical having from 2 to carbon atoms, when R is an alkoxy radical, R is 6 an acyloxy radical, and vice versa, and at least one compound of the formula:

wherein R and R are saturated alkoxy radicals of from 1 to 9 carbon atoms, and x and y differ and are selected from the group consisting of 0 and 1.

2. A nematic liquid crystal composition according to claim 1 wherein two compounds of the formula:

are present, each R is an alkoxy radical and each R is an alkyl radical.

3. A nematic liquid crystal composition according to claim 1 wherein two compounds of the formula:

are present, each R is an alkoxy radical and each R is an acyloxy radical.

4. A nematic liquid crystal composition according to claim 2 wherein said two compounds are N-(p-butoxybenzylidene) p propylaniline and N-(p-ethoxybenzylidene) -p-butylani1ine.

5. A nematic liquid crystal composition according to claim 3 wherein said two compounds are p-methoxybenzylidene p aminophenylbutyrate and p butoxybenzylidene-p-aminophenyl propionate.

6. A nematic liquid crystal composition according to claim 1 wherein said last indicated compound is butylp-(p-ethoxyphenoxycarbonyl) phenyl carbonate.

7. A nematic liquid crystal composition comprising p methoxybenzylidene p aminophenyl butyrate, pbutoxybenzylidene-p-aminophenyl propionate, butyl-p- (p-ethoxyphenoxycarbonyl) phenyl carbonate, N-(p butoxybenzylidene) p propylaniline, and N- (p-ethoxybenzylidene)-p-butylaniline.

8. A nematic liquid crystal composition having a very broad mesophase comprising a mixture of (a) at least one compound of Formula I:

wherein R is a saturated alkoxy radical having from 1 to 5 carbon atoms and R is an alkyl radical having from 2 to 6 carbon atoms;

(b) at least one compound of the Formula II:

wherein R is a saturated alkoxy radical having from 1 to 5 carbon atoms and R is a saturated acyloxy radical having from 2 to 4 carbon atoms; and

(c) at least one compound of the Formula III:

wherein R is a saturated alkoxy radical having from 1 to 5 carbon atoms and R is an alkyl radical having from 1 to 5 carbon atoms; the total amount of (a), (b), and (c) in said mixture being, respectively, from about 10 to about 20 weight percent, from about 60 to about weight percent, and from about 5 to about 20 weight percent.

9. A nematic liquid crystal composition as in claim 8, wherein portion (a) comprises N-(p-butoxybenzylidene)- p propylaniline and N (p-ethoxybenzylidene) p-butylaniline; (b) comprises p-meth'oxybenzylidene-p-aminophenyl butyrate and p-butoxybenzylidene-p-aminophenyl propionate; and portion (c) comprises butyl-p-(p-ethoxyphenoxycarbonyl) phenyl carbonate.

10. A nematic liquid crystal composition as in claim 9, wherein the compounds in said portion (a) are present in said composition in about equal amounts, the compounds in said portion (b) are present in said composition in a mole ratio of about 3:2, and the compound in said portion (0) is present in said composition in an amount about equal to one of the compounds in said portion (a).

11. A nematic liquid crystal composition as in claim 10, wherein said portion (a), said portion (b), and said portion (c) are present in said composition in weight ratio of about 6:16:3, respectively.

8 References Cited UNITED STATES PATENTS 9/1972 Jones 350-160 R OTHER REFERENCES Usol tseva et a1.: Chemical Characteristics, Structure and Properties of Liquid Crystal, Russian Chemical Reviews, vol. 32, No. 9, September 1963, pp. 495-507.

10 HAROLD ANSHER, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R.

15 23230 LC; 35016O LC 

